U.S. patent number 9,624,856 [Application Number 14/439,769] was granted by the patent office on 2017-04-18 for exhaust gas purification system and exhaust gas purification method.
This patent grant is currently assigned to ISUZU MOTORS LIMITED. The grantee listed for this patent is ISUZU MOTORS LIMITED. Invention is credited to Daiji Nagaoka, Takayuki Sakamoto.
United States Patent |
9,624,856 |
Nagaoka , et al. |
April 18, 2017 |
Exhaust gas purification system and exhaust gas purification
method
Abstract
An exhaust gas purification system with a diesel particulate
filter in an exhaust passage of an internal combustion engine. A
surface filtration cake layer formation enhancement control or a
particulate matter generation amount reduction control is
temporarily performed immediately after a forced regeneration
treatment on the diesel particulate filter. The system and a method
are directed to a particulate matter slip-through phenomenon in
which the particulate matter slip-through amount temporarily
increases immediately after particulate matter re-combustion in a
forced regeneration treatment on the diesel particulate filter. The
diesel particulate filter is disposed in the exhaust passage of the
internal combustion engine and reduces the total amount of
particulate matter emitted to the atmosphere immediately after the
particulate matter re-combustion in the forced regeneration
treatment on the diesel particulate filter.
Inventors: |
Nagaoka; Daiji (Kamakura,
JP), Sakamoto; Takayuki (Fujisawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
ISUZU MOTORS LIMITED |
Tokyo |
N/A |
JP |
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|
Assignee: |
ISUZU MOTORS LIMITED (Tokyo,
JP)
|
Family
ID: |
50776059 |
Appl.
No.: |
14/439,769 |
Filed: |
November 19, 2013 |
PCT
Filed: |
November 19, 2013 |
PCT No.: |
PCT/JP2013/081101 |
371(c)(1),(2),(4) Date: |
April 30, 2015 |
PCT
Pub. No.: |
WO2014/080877 |
PCT
Pub. Date: |
May 30, 2014 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20150292425 A1 |
Oct 15, 2015 |
|
Foreign Application Priority Data
|
|
|
|
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Nov 26, 2012 [JP] |
|
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2012-257190 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D
41/40 (20130101); F02D 41/029 (20130101); F02D
41/0055 (20130101); F01N 9/002 (20130101); F02D
41/0235 (20130101); F02M 26/15 (20160201); F02D
21/08 (20130101); F01N 3/023 (20130101); F01N
3/035 (20130101); F01N 3/0253 (20130101); F01N
11/00 (20130101); F02M 26/23 (20160201); F02D
2200/0812 (20130101); Y02T 10/40 (20130101); F02M
26/05 (20160201); Y02T 10/47 (20130101); Y02T
10/44 (20130101) |
Current International
Class: |
F01N
3/00 (20060101); F01N 9/00 (20060101); F02D
21/08 (20060101); F01N 3/023 (20060101); F01N
3/035 (20060101); F01N 3/025 (20060101); F02D
41/00 (20060101); F02D 41/40 (20060101); F02D
41/02 (20060101); F01N 3/02 (20060101); F02M
26/15 (20160101); F01N 11/00 (20060101); F02M
26/05 (20160101); F02M 26/23 (20160101) |
Field of
Search: |
;60/278,285,295,297,311 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
10 2010 017 575 |
|
Feb 2012 |
|
DE |
|
2007-56750 |
|
Mar 2007 |
|
JP |
|
2007-230302 |
|
Sep 2007 |
|
JP |
|
2009-7982 |
|
Jan 2009 |
|
JP |
|
2010-31799 |
|
Feb 2010 |
|
JP |
|
2011-149357 |
|
Aug 2011 |
|
JP |
|
2012-154255 |
|
Aug 2012 |
|
JP |
|
Other References
International Search Report mailed on Mar. 4, 2014 in corresponding
International Patent Application No. PCT/JP2013/081101. cited by
applicant .
Japanese Platform for Patent Information English Abstract of
Japanese Publication No. 2007-56750, Published Mar. 8, 2007. cited
by applicant .
Japanese Platform for Patent Information English Abstract of
Japanese Publication No. 2007-230302, Published Sep. 13, 2007.
cited by applicant .
Japanese Platform for Patent Information English Abstract of
Japanese Publication No. 2010-31799, Published Feb. 12, 2010. cited
by applicant .
Japanese Platform for Patent Information English Abstract of
Japanese Publication No. 2011-149357, Published Aug. 4, 2011. cited
by applicant .
Extended European Search Report dated Jun. 28, 2016 in
corresponding European Patent Application No. 13857648.3. cited by
applicant.
|
Primary Examiner: Trieu; Thai Ba
Assistant Examiner: Tran; Diem
Attorney, Agent or Firm: Staas & Halsey LLP
Claims
The invention claimed is:
1. An exhaust gas purification system comprising: a diesel
particulate filter disposed in an exhaust passage of an internal
combustion engine; and a controller configured to determine a
particulate amount generated in the internal combustion engine by
comparing a preset particulate matter generation amount database
with a detected engine operation state, determine a particulate
matter slip amount passing through the diesel particulate filter by
comparing the preset particulate matter generation amount database
with a preset particulate matter trap efficiency database,
recombust particulate matter using a forced regeneration treatment
of the diesel particulate filter, and temporarily perform a surface
filtration cake layer formation enhancement control or a
particulate matter generation amount reduction control based on the
determined particulate matter generation amount and the determined
particulate matter slip-through amount, immediately after the
particulate matter re-combustion using the forced regeneration
treatment on the diesel particulate filter, wherein, when both the
determined particulate matter generation amount and the determined
particulate matter slip-through amount are smaller than respective
preset thresholds, the surface filtration cake layer formation
enhancement control is performed.
2. The exhaust gas purification system according to claim 1,
wherein the surface filtration cake layer formation enhancement
control includes performing one of a particulate matter generation
amount increase control by increasing an exhaust gas recirculation
rate, a retard control in which fuel injection timing is retarded
in in-cylinder fuel injection, or an air-fuel ratio richness
control in which an air-fuel ratio is made rich in in-cylinder fuel
injection.
3. The exhaust gas purification system according to claim 2,
wherein the retard control is performed, when an engine torque of
the internal combustion engine is lower than a preset first setting
value, the exhaust gas recirculation rate increase control is
performed, when the engine torque is not lower than the preset
first setting value but lower than a preset second setting value,
and the air-fuel ratio richness control is performed, when the
engine torque is not lower than the preset second setting
value.
4. The exhaust gas purification system according to claim 2,
wherein the particulate matter generation amount reduction control
is a particulate matter generation amount limiting control
performed by decreasing an exhaust gas recirculation rate.
5. The exhaust gas purification system according to claim 1,
wherein the particulate matter generation amount reduction control
is a particulate matter generation amount limiting control by
decreasing an exhaust gas recirculation rate.
6. The exhaust gas purification system according to claim 5,
wherein the retard control is performed, when an engine torque of
the internal combustion engine is lower than a preset first setting
value, the exhaust gas recirculation rate increase control is
performed, when the engine torque is not lower than the preset
first setting value but lower than a preset second setting value,
and the air-fuel ratio richness control is performed, when the
engine torque is not lower than the preset second setting
value.
7. An exhaust gas purification method, comprising: purifying
exhaust gas of an internal combustion engine with a diesel
particulate filter; performing particulate matter re-combustion by
a forced regeneration treatment on the diesel particulate filter;
determining a particulate matter amount generated in the internal
combustion engine by comparing a preset particulate matter
generation amount database with a detected engine operation state;
determining a particulate matter slip through amount passing
through the diesel particulate filter by comparing the preset
particulate matter generation amount database with a preset
particulate matter trap efficiency database; and temporarily
performing a surface filtration cake layer formation enhancement
control or a particulate matter generation amount reduction control
based on the determined particulate matter generation amount and
the determined particulate matter slip-through amount immediately
after the particulate matter re-combustion by the forced
regeneration treatment on the diesel particulate filter, wherein,
when both the determined particulate matter generation amount and
the determined particulate matter slip-through amount are smaller
than respective preset thresholds, the surface filtration cake
layer formation enhancement control is performed.
8. The exhaust gas purification method according to claim 7,
wherein the temporarily performing the surface filtration cake
layer formation control includes one of a particulate matter
generation amount increase control by increasing an exhaust gas
recirculation rate, a retard control in which fuel injection timing
is retarded in in-cylinder fuel injection, or an air-fuel ratio
richness control in which an air-fuel ratio is made rich in
in-cylinder fuel injection is performed as the surface filtration
cake layer formation enhancement control.
9. The exhaust gas purification method according to claim 8,
wherein the retard control is performed, when an engine torque of
the internal combustion engine is lower than a preset first setting
value, the exhaust gas recirculation rate increase control is
performed, when the engine torque is not lower than the preset
first setting value but lower than a preset second setting value,
and the air-fuel ratio richness control is performed, when the
engine torque is not lower than the preset second setting
value.
10. The exhaust gas purification method according to claim 8,
further comprising: wherein a particulate matter generation amount
limiting control by decreasing an exhaust gas recirculation rate is
performed as the particulate matter generation amount reduction
control.
11. The exhaust gas purification method according to claim 7,
further comprising: performing, as the particulate matter
generation amount reduction control, a particulate matter
generation amount limiting control by decreasing an exhaust gas
recirculation rate.
12. The exhaust gas purification method according to claim 11,
wherein the retard control is performed, when an engine torque of
the internal combustion engine is lower than a preset first setting
value, the exhaust gas recirculation rate increase control is
performed, when the engine torque is not lower than the preset
first setting value but lower than a preset second setting value,
and the air-fuel ratio richness control is performed, when the
engine torque is not lower than the preset second setting
value.
13. An exhaust gas purification system comprising: a diesel
particulate filter disposed in an exhaust passage of an internal
combustion engine, wherein a surface filtration cake layer
formation enhancement control or a particulate matter generation
amount reduction control is temporarily performed immediately after
particulate matter re-combustion in a forced regeneration treatment
on the diesel particulate filter, wherein the surface filtration
cake layer formation enhancement control is one of a particulate
matter generation amount increase control by increasing an exhaust
gas recirculation rate, a retard control in which fuel injection
timing is retarded in in-cylinder fuel injection, or an air-fuel
ratio richness control in which an air-fuel ratio is made rich in
in-cylinder fuel injection, wherein the retard control is
performed, when an engine torque of the internal combustion engine
is lower than a preset first setting value, the exhaust gas
recirculation rate increase control is performed, when the engine
torque is not lower than the preset first setting value but lower
than a preset second setting value, and the air-fuel ratio richness
control is performed, when the engine torque is not lower than the
preset second setting value, and wherein the particulate matter
generation amount reduction control is a particulate matter
generation amount limiting control by decreasing an exhaust gas
recirculation rate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. National Stage Application, which claims
the benefit under 35 U.S.C. .sctn.371 of PCT International Patent
Application No. PCT/JP2013/081101, filed Nov. 19, 2013, which
claims the foreign priority benefit under 35 U.S.C. .sctn.119 of
Japanese Patent Application No. 2012-257190, filed Nov. 26, 2012,
the contents of which are incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to an exhaust gas purification system
and an exhaust gas purification method capable of preventing
particulate matter ("PM") slip-through which occurs in an exhaust
gas purification system including a diesel particulate filter
("DPF") disposed in an exhaust passage of an internal combustion
engine immediately after PM re-combustion in a forced regeneration
treatment on the DPF, to reduce the total amount of PMs emitted to
the atmosphere.
BACKGROUND ART
To remove PMs in exhaust gas emitted through an exhaust passage of
an internal combustion engine to the outside of a vehicle, an
exhaust gas purification system has been used in which a DPF that
traps PMs is provided in the exhaust passage of the internal
combustion engine. With the increase in amount of PMs trapped in
the DPF, the pressure drop across the DPF increases to deteriorate
the fuel-efficiency, or the amount of PMs which exceed the
limitation of the PM trap and which slip through the DPF increases
to deteriorate the emission performance. For these reasons, a
forced regeneration treatment for the re-combustion of the trapped
PMs is performed on the DPF by raising the temperature of the DPF
at regular intervals to reduce the amount of PMs emitted to the
atmosphere. By employing the DPF, the amount of PMs emitted to the
atmosphere is reduced to a level of about 1/100.
However, as shown in FIG. 11, the DPF has a problem in that a
phenomenon occurs in which the amount of PMs emitted to the
atmosphere temporarily increases (the DPF outlet soot concentration
increases in FIG. 11) because of "PM slip-through (soot
break-through)" in which PMs pass through the DPF after the
re-combustion of PMs in the forced regeneration treatment on the
DPF. This phenomenon is thought to occur as follows.
For example, in a wall flow type DPF, when PMs pass through a wall
surface that sections cells, the PMs are trapped on the wall
surface. Here, PMs with relatively large particle sizes do not pass
through the wall surface, but are attached to a front side
(upstream side) of the wall surface to form a surface filtration
cake layer. The formation of the surface filtration cake layer
increases the pressure drop to some degree, but simultaneously the
PM trap efficiency is also improved. However, the surface
filtration cake layer is combusted and lost by the PM re-combustion
in the forced regeneration treatment on the DPF, and hence the PM
slip-through (blow off) occurs in which the PM trap efficiency is
temporarily lowered. As a result, PMs are not trapped by the DPF,
but slip through the DPF, so that the amount of PMs emitted to the
atmosphere increases temporarily.
Note that, when the temperature of the DPF raised by the forced
regeneration treatment drops after the PM re-combustion, PMs are
again trapped by the DPF to form the surface filtration cake layer
again on the front side of the wall surface. With the growth of the
surface filtration cake layer, the PM trap efficiency increases,
which leads to the decrease in the PM slip-through amount, and in
turn, the decrease in the amount of PMs emitted to the
atmosphere.
The degree of the deterioration in the PM removal due to the
temporary increase in the amount of PMs emitted to the atmosphere
caused by the PM slip-through is not detectable with eyes. However,
the PM slip-through may cause the deterioration in the K-factor,
which is a deterioration factor listed in an application for the
certification of the emission performance, and the like. Hence, a
countermeasure has to be taken against the PM slip-through.
As a countermeasure against the PM slip-through, the present
inventors have proposed a DPF regenerator as described in Japanese
patent application Kokai publication No. 2011-149357, for example.
Specifically, to reduce the soot break-through in which PMs slip
through a DPF because of the decrease (blow-off) in the PM trap
efficiency immediately after DPF regeneration in an exhaust gas
apparatus in which the DPF is provided in an exhaust gas flow
passage of an internal combustion engine, post injection which is
performed in a forced regeneration of the DPF is prohibited and the
forced regeneration of the DPF is stopped at a time point where the
PM concentration detected downstream of the DPF is not lower than a
predetermined value and the blow-off occurs in the DPF. Thus, the
temporary increase in the amount of PMs emitted to the atmosphere
due to the post injection is suppressed.
In this DPF regenerator, the post injection of the forced
regeneration treatment on the DPF is stopped at the same time as
the occurrence of the blow-off in the DPF. This prevents PMs
generated because of the post injection performed for the forced
regeneration treatment on the DPF from being emitted to the
atmosphere during the blow-off immediately after the PM
re-combustion. Thus, the increase in the amount of PMs emitted to
the atmosphere is suppressed.
PRIOR ART DOCUMENT
Patent Document 1: Japanese patent application Kokai publication
No. 2011-149357
SUMMARY OF THE INVENTION
The present inventors have found that it is necessary to perform
not only the passive countermeasure proposed for the DPF apparatus
in which the post injection performed in the forced regeneration
treatment on the DPF is stopped at the same time as the completion
of the PM re-combustion to eliminate the amount of PMs generated by
the post injection at the occurrence of the PM slip-through
phenomenon, but also an active suppression of the increase in the
amount of PMs emitted to the atmosphere after the completion of the
PM re-combustion in the forced regeneration treatment on the DPF.
This finding leads the present inventors to the present
invention.
The present invention has been made in view of the above-described
matters, and an object of the present invention is to provide an
exhaust gas purification system and an exhaust gas purification
method which are directed to the PM slip-through phenomenon in
which the PM slip-through amount temporarily increases immediately
after PM re-combustion in a forced regeneration treatment on a DPF
in an exhaust gas purification system including the DPF disposed in
an exhaust passage of an internal combustion engine, and which are
capable of reducing the total amount of PMs emitted to the
atmosphere immediately after the PM re-combustion in the forced
regeneration treatment on the DPF, and reducing the total amount of
PMs emitted to the atmosphere.
An exhaust gas purification system according to the present
invention to achieve the above-described object is an exhaust gas
purification system including a DPF disposed in an exhaust passage
of an internal combustion engine, wherein the exhaust gas
purification system is configured to temporarily perform a surface
filtration cake layer formation enhancement control or a PM
generation amount reduction control, immediately after PM
re-combustion in a forced regeneration treatment on the DPF.
Note that the term "temporarily" indicates a period having a
relationship with a period for which the phenomenon (blow-off) in
which the amount of PMs emitted to the atmosphere temporarily
increases occurs. As the temporary period, it is possible to employ
a period of a preset time (for example, 5 minutes or the like), a
period until a cumulative PM trap amount becomes not less than a
preset amount, a period until a PM trap efficiency becomes not less
than a predetermined ratio, a period until a PM slip-through amount
becomes not less than a predetermined amount, a period until a PM
slip-through ratio becomes not less than a predetermined value, or
the like.
With this configuration, the phenomenon (blow-off) in which the
amount of PMs passing through the DPF temporarily increases, and
the amount of PMs emitted to the atmosphere temporarily increases
immediately after the PM re-combustion in the forced regeneration
treatment of PMs in the DPF can be treated as follows.
Specifically, during the period for which this phenomenon
continues, early formation and growth of the surface filtration
cake layer on the wall surface of the DPF are enhanced immediately
after the PM re-combustion of the forced regeneration treatment by
the surface filtration cake layer formation enhancement control in
which the PM generation amount is increased from that generated
during an ordinary operation. In this manner, the PM slip-through
amount can be reduced, and the total amount of PMs emitted to the
atmosphere can be reduced.
Alternatively, by the PM generation amount reduction control in
which the PM generation amount is reduced from that generated
during an ordinary operation, the PM generation amount in the
internal combustion engine is reduced for a temporary period until
the surface filtration cake layer has grown. Thus, the amount of
PMs flowing into the DPF is reduced, and the DPF slip-through
amount is reduced, so that the total amount of PMs emitted to the
atmosphere can be reduced.
When the above-described exhaust gas purification system is
configured such that the surface filtration cake layer formation
enhancement control is any one of a PM generation amount increase
control by increasing an exhaust gas recirculation ("EGR") rate, a
retard control in which fuel injection timing is retarded in
in-cylinder fuel injection, or an air-fuel ratio richness control
in which an air-fuel ratio is made rich in in-cylinder fuel
injection, the following effects can be achieved.
Specifically, with this configuration, when the PM generation
amount increase control by increasing an EGR rate is performed, the
in-cylinder combustion temperature is lowered by increasing the EGR
rate, so that the amount of soot formed is slightly increased, and
HCs are adsorbed onto the soot particles by increasing the HC
concentration to increase the particle diameters of the soot. Thus,
the formation of the surface filtration cake layer can be
enhanced.
Meanwhile, when each of the retard control in which fuel injection
timing is retarded in in-cylinder fuel injection and the air-fuel
ratio richness control (rich-spike control or the like) in which an
air-fuel ratio is made rich in in-cylinder fuel injection is
conducted, the HC components (hydrocarbon components) in the
exhaust gas are increased by the control, and the HCs are attached
to the PMs to increase the particle diameters. This can facilitate
the trapping of the PMs on the wall surface of the DPF, and hence
the formation of the surface filtration cake layer can be
enhanced.
Note that, to increase the effect to enhance the formation of the
surface filtration cake layer, it is more preferable to monitor the
temperature of the DPF and perform each of the retard control and
the air-fuel ratio richness control at a temperature where the HCs
do not vaporize into a gas phase state, and the HCs can be attached
to the wall surface of the DPF, while remaining in a liquid phase
state in which the HCs can be easily attached to the PMs.
When the above-described exhaust gas purification system is
configured such that the PM generation amount reduction control is
a PM generation amount limiting control by decreasing an EGR rate,
the in-cylinder combustion temperature can be raised by the PM
generation amount limiting control by decreasing an EGR rate to
reduce the PM generation amount, so that the amount of PMs slipping
through the DPF can be reduced. Thus, the PM slip-through amount
can be reduced, until the surface filtration cake layer is formed
to some extent.
The above-described exhaust gas purification system is configured
such that, in the surface filtration cake layer formation
enhancement control, the retard control is performed, when an
engine torque of the internal combustion engine is lower than a
preset first setting value, the EGR rate increase control is
performed, when the engine torque is not lower than the first
setting value but lower than a preset second setting value, and the
air-fuel ratio richness control is performed, when the engine
torque is not lower than the second setting value. With this
configuration, an optimum surface filtration cake layer formation
enhancement control can be selected according to the engine torque
(engine output) of the internal combustion engine. Hence, while
adverse influences on the engine torque and the emission
performance are reduced, the formation of the surface filtration
cake layer can be enhanced efficiently, and the total amount of PMs
emitted to the atmosphere can be reduced.
The above-described exhaust gas purification system is configured
such that the PM generation amount reduction control is performed,
when a PM generation amount which is a generation amount of PMs
generated in the internal combustion engine exceeds a preset
acceptable PM generation amount, or when a PM slip-through amount
which is an amount of PMs passing through the DPF exceeds a preset
acceptable PM slip-through amount, immediately after the PM
re-combustion in the forced regeneration treatment on the DPF. With
this configuration, the PM generation amount reduction control is
performed on the basis of the PM generation amount or the PM
slip-through amount. Hence, the total amount of PMs emitted to the
atmosphere can be reduced reliably.
The PM generation amount, which is the generation amount of PMs
generated in the internal combustion engine immediately after the
PM re-combustion of the forced regeneration treatment on the DPF,
is preferably calculated as follows. Specifically, data on the PM
generation amount are acquired in advance on the basis of an engine
operation state of the internal combustion engine to create a PM
generation amount database. Then, the PM generation amount is
calculated from an engine operation state immediately after the
forced regeneration treatment on the DPF with reference to the PM
generation amount database. With this configuration, the PM
generation amount can be precisely calculated on the basis of the
preset PM generation amount database.
Meanwhile, the PM slip-through amount, which is an amount of PMs
passing through the DPF immediately after the PM re-combustion of
the forced regeneration treatment on the DPF, is preferably
calculated as follows. Specifically, data on the PM trap efficiency
from the time point immediately after the PM re-combustion are
acquired in advance on the basis of the cumulative PM trap amount
to create a PM trap efficiency database. Then, the PM generation
amount is calculated from the engine operation state immediately
after the forced regeneration treatment on the DPF with reference
to the PM generation amount database. In addition, the PM trap
amount is calculated from the PM trap efficiency (which is derived
from the preceding cumulative PM trap amount), and a cumulative PM
trap amount which is a cumulative value of the PM trap amount is
calculated. Then, the PM slip-through amount is calculated by
subtracting the PM trap amount from the PM generation amount. With
this configuration, the PM slip-through amount can be calculated
precisely on the basis of the preset PM generation amount database
and the preset PM trap efficiency database.
In addition, an exhaust gas purification method of the present
invention to achieve the above-described object is an exhaust gas
purification method including purifying exhaust gas of an internal
combustion engine with a DPF, wherein a surface filtration cake
layer formation enhancement control or a PM generation amount
reduction control is temporarily performed immediately after PM
re-combustion in a forced regeneration treatment on the DPF.
In the exhaust gas purification method, any one of a PM generation
amount increase control by increasing an EGR rate, a retard control
in which fuel injection timing is retarded in in-cylinder fuel
injection, and an air-fuel ratio richness control in which an
air-fuel ratio is made rich in in-cylinder fuel injection is
performed as the surface filtration cake layer formation
enhancement control.
In addition, in the above-described exhaust gas purification
method, a PM generation amount limiting control by decreasing an
EGR rate is performed as the PM generation amount reduction
control.
Moreover, in the surface filtration cake layer formation
enhancement control in the above-described exhaust gas purification
method, the retard control is performed, when an engine torque of
the internal combustion engine is lower than a preset first setting
value, the EGR rate increase control is performed, when the engine
torque is not lower than the first setting value but lower than a
preset second setting value, and the air-fuel ratio richness
control is performed, when the engine torque is not lower than the
second setting value.
In addition, in the above-described exhaust gas purification
method, the PM generation amount reduction control is performed,
when a PM generation amount which is a generation amount of PMs
generated in the internal combustion engine exceeds a preset
acceptable PM generation amount, or when a PM slip-through amount
which is an amount of PMs passing through the DPF exceeds a preset
acceptable PM slip-through amount, immediately after the PM
re-combustion in the forced regeneration treatment on the DPF.
These exhaust gas purification methods can achieve the same effects
as those of the above-described exhaust gas purification
systems.
The exhaust gas purification system and the exhaust gas
purification method of the present invention are directed to the PM
slip-through (blow-off) phenomenon in which the PM slip-through
amount temporarily increases immediately after the PM re-combustion
of the forced regeneration treatment on a DPF in an exhaust gas
purification system comprising the DPF disposed in an exhaust
passage of an internal combustion engine. According to the exhaust
gas purification system and the exhaust gas purification method of
the present invention, the early reformation and growth of the
surface filtration cake layer on the wall surface of the DPF are
temporarily enhanced by the surface filtration cake layer formation
enhancement control in which the PM generation amount is increased,
or the PM generation amount from the internal combustion engine is
reduced and the amount of PMs flowing into the DPF is reduced by
the PM generation amount reduction control in which the PM
generation amount is reduced for a temporary period until the
surface filtration cake layer is formed again and has grown. Thus,
it is possible to reduce the total amount of PMs emitted to the
atmosphere immediately after the PM re-combustion in the forced
regeneration treatment on the DPF, and reduce the total amount of
PMs emitted to the atmosphere.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a configuration of an exhaust gas purification system
of an embodiment according to the present invention.
FIG. 2 shows a configuration of control means of the exhaust gas
purification system of an embodiment according to the present
invention.
FIG. 3 shows an example of a control flow of an exhaust gas
purification method of an embodiment according to the present
invention.
FIG. 4 shows details of a control step S20 in FIG. 3.
FIG. 5 is a schematic diagram of an engine outlet PM generation
amount map during ordinary combustion.
FIG. 6 is a schematic diagram of an engine outlet PM generation
amount map during a retard control.
FIG. 7 is a schematic diagram of an engine outlet PM generation
amount map during an EGR rate increase control.
FIG. 8 is a schematic diagram of an engine outlet PM generation
amount map during an air-fuel ratio richness control.
FIG. 9 is a schematic diagram of a PM trap efficiency map.
FIG. 10 shows an example of a time series of a PM slip-through
amount (soot concentration) in an Example and a Conventional
Example.
FIG. 11 shows an example of a time series of a PM slip-through
amount (DPF outlet soot concentration) after forced regeneration of
a DPF of a conventional technology.
Hereinafter, an exhaust gas purification system and an exhaust gas
purification method of an embodiment according to the present
invention are described with reference to the drawings. As shown in
FIG. 1, an exhaust gas purification system 1 of this embodiment
includes an intake passage 12 connected to an intake manifold 11a
of an engine main body 11 of an engine (internal combustion engine)
10, an exhaust passage 13 connected to an exhaust manifold 11b, and
an EGR passage 14 which connects the exhaust manifold 11b and the
intake manifold 11a to each other.
The intake passage 12 is provided with a compressor 15a of a
turbosupercharger (turbo charger) 15, an intercooler 16, and an
intake throttle (intake valve) 17 in this order from an upstream
side. Intake air A passes thorough an air cleaner and an intake air
mass flow sensor (MAF), is compressed by the compressor 15a, and
further cooled in the intercooler 16, passes through the intake
throttle 17 which regulates the amount of the intake air, and is
supplied to the intake manifold 11a.
Meanwhile, the exhaust passage 13 is provided with a turbine 15b of
the turbosupercharger 15, an in-exhaust passage fuel injection
valve 18, and an exhaust gas purification apparatus 19, in this
order from the upstream side. The exhaust gas purification
apparatus 19 includes an oxidation catalyst (DOC: diesel oxidation
catalyst) 19a on the upstream side and a DPF (diesel particulate
filter) 19b on the downstream side. PMs (particulate matters) in
exhaust gas G are trapped in the DPF 19b. When the PM trap amount
increases, a forced regeneration treatment of the DPF 19b is
performed. In the PM re-combustion in the forced regeneration
treatment on the DPF 19b, fuel f is supplied into the exhaust gas G
from the in-exhaust passage fuel injection valve 18. The fuel f is
oxidized with the oxidation catalyst 19a, and the temperatures of
the exhaust gas G and the DPF 19b are raised by the heat of
combustion of the fuel f to conduct a re-combustion treatment of
the PMs trapped in the DPF 19b.
Meanwhile, the EGR passage 14 is provided with an EGR cooler 20 and
an EGR valve 21 in this order from the upstream side. During EGR
(exhaust gas recirculation), EGR gas Ge, which is part of the
exhaust gas G, is introduced through the exhaust manifold 11b. The
EGR gas Ge is cooled in the EGR cooler 20, then passes through the
EGR valve 21 which regulates the amount of the EGR gas, and then is
supplied to the intake manifold 11a.
In addition, a first exhaust gas temperature sensor 22 is provided
on an upstream side of the oxidation catalyst 19a, a second exhaust
gas temperature sensor 23 is provided between the oxidation
catalyst 19a and the DPF 19b, and a differential pressure sensor 24
is provided for measuring a differential pressure between the
upstream side and the downstream side of the DPF 19b. Signals
detected by these sensors are inputted to a controlling device 30
called an engine control unit (ECU) which controls operation of the
engine 10 and the exhaust gas purification system 1. The
controlling device 30 receives signals detected by these sensors
and other various sensors such as an accelerator sensor, an engine
rotation sensor, and a cooling water sensor, and controls the
intake throttle 17, the in-exhaust passage fuel injection valve 18,
the EGR valve 21, and the like according to operation conditions of
the engine 10, a state of the exhaust gas G, and the like.
The DPF 19b disposed in the exhaust passage 13 of the exhaust gas
purification system 1 traps PMs contained in the exhaust gas G
flowing through the exhaust passage 13. Here, as the trap amount of
PMs trapped in the DPF 19b increases, the pressure drop across the
DPF 19b increases, which causes lowering of the fuel-efficiency and
the like, and the trap amount exceeds the PM trap capacity, so that
the amount of PMs that slip through the DPF 19b increases. For this
reason, the DPF 19b is regenerated by performing the forced
regeneration treatment for the re-combustion of the trapped PMs at
regular intervals or upon detection that the PM trap amount exceeds
an acceptable amount or that the differential pressure across the
DPF 19b exceeds an acceptable amount.
However, immediately after the re-combustion of the trapped PMs by
the forced regeneration treatment on the DPF 19b, a surface
filtration cake layer, which is an aggregate of PMs having large
particle diameters such as HCs and is formed on a front side of a
wall surface of the DPF 19b through which the exhaust gas G passes
is lost, and hence a blow-off phenomenon occurs temporarily in
which PMs slip through the DPF 19b.
Here, to address the phenomenon in which the amount of PMs passing
through the DPF 19b temporarily increases, and consequently the
amount of PMs emitted to the atmosphere temporarily increases,
immediately after the PM re-combustion by the forced regeneration
treatment of PMs in the DPF 19b, the controlling device 30 of the
present invention includes, as shown in FIG. 2, slip-through amount
limiting means M30 as means for performing the surface filtration
cake layer formation enhancement control or the PM generation
amount reduction control, immediately after the forced regeneration
treatment on the DPF 19b temporarily until the surface filtration
cake layer is formed again and has grown to a certain extent. The
slip-through amount limiting means M30 includes PM re-combustion
completion detection means M31, surface filtration cake layer
formation enhancement control means M32, PM generation amount
calculation means M33, PM slip-through amount calculation means
M34, PM generation amount reduction control means M35, and surface
filtration cake layer reformation detection means M36.
The PM re-combustion completion detection means M31 is means for
detecting whether the PM re-combustion by the forced regeneration
treatment of PMs in the DPF 19b is completed. For example, the PM
re-combustion completion detection means M31 is configured to
determine that the PM re-combustion is completed at a time point
where a value .DELTA.P detected by the differential pressure sensor
24 becomes smaller than a preset setting value .DELTA.Pc, or to
determine that the PM re-combustion is completed at a time point
where a PM concentration difference .DELTA.Cpm across the DPF 19b
or a PM trap efficiency .eta.y calculated from the PM concentration
difference .DELTA.Cpm becomes smaller than the corresponding preset
value .DELTA.Cpm1 or .eta.y1.
Meanwhile, the surface filtration cake layer formation enhancement
control means M32 is means for performing a control for increasing
the amount of PMs (main components thereof are HCs and the like)
passing through the DPF 19b by increasing the amount (PM generation
amount) of PMs in the exhaust gas G at an outlet of the engine 10.
The surface filtration cake layer formation enhancement control
enhances early formation and growth of the surface filtration cake
layer on the wall surface of the DPF 19b immediately after the
forced regeneration treatment. Thus, the PM slip-through amount Y
is reduced, and the total amount of PMs emitted to the atmosphere
is reduced. Note that the PM slip-through amount Y before the
formation of the surface filtration cake layer is increased by
performing the surface filtration cake layer formation enhancement
control. However, since the surface filtration cake layer is formed
early, the total amount of PMs emitted to the outside air is
smaller than that in a conventional technology.
The surface filtration cake layer formation enhancement control
means M32 includes retard control means M32a for monitoring a
temperature of the DPF 19b and retarding fuel injection timing in
in-cylinder fuel injection when the DPF temperature is not higher
than a preset temperature, EGR rate increase control means M32b for
increasing the PM generation amount by increasing an EGR rate, and
air-fuel ratio richness control means M32c for monitoring the
temperature of the DPF 19b and making an air-fuel ratio rich in
in-cylinder fuel injection, when the DPF temperature is not higher
than a preset temperature. By performing any of these means M32a,
M32b, and M32c, the amount (PM generation amount) X of PMs in the
exhaust gas G at the outlet of the engine 10 is increased.
The retard control means M32a monitors the temperature of the DPF
19b, and performs the retard control in which the fuel injection
timing is retarded in in-cylinder fuel injection, when the DPF
temperature is not higher than the preset temperature. Hence, the
HC components in the exhaust gas G are increased at a DPF
temperature where the HC components in the exhaust gas G do not
vaporize into a gas phase state, and the particle diameters of the
PMs are increased by attaching the HCs in the liquid phase state to
the PMs. This can facilitate the trapping of the PMs on the wall
surface of the DPF 19b. Hence, the formation of the surface
filtration cake layer can be enhanced.
Meanwhile, in the case where the EGR rate increase control means
M32b performs the control for increasing the PM generation amount X
by increasing the EGR rate, an in-cylinder combustion temperature
in a cylinder, the exhaust gas temperature, and the DPF temperature
are lowered by increasing the EGR rate, and the PM generation
amount X is increased. Thus, the PM trap efficiency .eta.y by the
DPF 19b is increased, and the formation of the surface filtration
cake layer can be enhanced.
Meanwhile, the air-fuel ratio richness control means M32c monitors
the temperature of the DPF 19b, and performs the air-fuel ratio
richness control (rich-spike control or the like) in which the
air-fuel ratio is made rich in in-cylinder fuel injection when the
DPF temperature is not higher than the preset temperature. In this
case, as in the case of the retard control, the HC components in
the exhaust gas G are increased at a DPF temperature where the HC
components in the exhaust gas G do not vaporize into a gas phase
state, and the particle diameters of the PMs are increased by
attaching HCs in a liquid phase state to the PMs. This can
facilitate the trapping of the PMs on the wall surface of the DPF
19b. Thus, the formation of the surface filtration cake layer can
be enhanced.
In other words, the PMs are further converted to soot which is
readily accumulated on a surface layer of the wall surface of the
DPF 19b. PM particles which more readily form the surface
filtration cake layer by being trapped on the wall surface are
presumably wet PMs having relatively large particle diameters on
which HCs and the like are adsorbed. In this respect, with the DPF
temperature being monitored, the air-fuel ratio is made rich by
temporarily retarding the injection timing or temporarily
performing rich-spike, when the temperature drops. Thus, HC
components are increased among the exhaust gas components, and the
HCs are attached to PMs to increase the particle diameters, which
facilitates the trapping of the PMs on the wall surface of the DPF
19b.
Note that, in addition to the above-described means M32a, M32b, and
M32c, any means capable of making it easier for the PMs to be
trapped on the front side of the wall surface of the DPF 19b, and
thus enhancing the formation of the surface filtration cake layer,
can be employed for the surface filtration cake layer formation
enhancement control.
In addition, among these surface filtration cake layer formation
enhancement controls, the retard control by the retard control
means M32a is performed in a case of a low-load region where an
engine torque T of the engine 10 is lower than a preset first
setting value T1, and the change in the smoke concentration is
insensitive to the EGR rate; the EGR rate increase control by the
EGR rate increase control means M32b is performed in a case of a
middle-load region where the engine torque T is not lower than the
first setting value T1 but lower than a preset second setting value
T2, and the change in the smoke concentration is sensitive to the
EGR rate; and the air-fuel ratio richness control by the air-fuel
ratio richness control means M32c is performed in a case of a
high-load region where the engine torque T is not lower than the
second setting value T2, and a change in the timing of the
in-cylinder fuel injection or a change in the EGR rate tends to
exert an influence on the power performance of the engine 10.
With this configuration, optimum means for the surface filtration
cake layer formation enhancement control can be selected from the
means M32a, M32b, and M32c according to the engine torque (engine
output) of the engine 10. Hence, while adverse influences on the
engine torque T and the emission performance are reduced, the
formation of the surface filtration cake layer can be enhanced
efficiently, and the total amount of PMs emitted to the atmosphere
can be reduced.
Meanwhile, the PM generation amount calculation means M33 is means
for calculating the PM generation amount X generated at the outlet
of the engine 10 immediately after the forced regeneration
treatment on the DPF 19b. Data on the PM generation amount X at the
outlet of the engine 10, for example, at an outlet of the exhaust
manifold 11b or the like are acquired in advance on the basis of
the engine operation state of the engine 10, and a PM generation
amount database is created. Then, with reference to the PM
generation amount database, the PM generation amount X is
calculated from an engine operation condition, for example, an
engine rotation speed or an engine torque (or an in-cylinder fuel
injection amount), immediately after the forced regeneration
treatment on the DPF 19b. This makes it possible to precisely
calculate the PM generation amount on the basis of the preset PM
generation amount database.
As examples of the database, FIG. 5 shows an engine outlet PM
generation amount map during ordinary combustion, FIG. 6 shows an
engine outlet PM generation amount map during a retard control,
FIG. 7 shows an engine outlet PM generation amount map during an
EGR rate increase control, and FIG. 8 shows an engine outlet PM
generation amount map during an air-fuel ratio richness control.
These engine outlet PM generation amount maps can be created by
measuring the PM amount at the engine outlet with the engine
rotation speed (the engine speed) and the fuel flow rate
(equivalent to the engine torque or the load) being varied in a
bench test or the like, or other methods. In other words, a map of
the amount X of PMs generated at the engine outlet is
experimentally created in advance.
Meanwhile, the PM slip-through amount calculation means M34 is
means for calculating the amount of PMs slipping through the DPF
19b, i.e., the PM slip-through amount Y. For calculating the PM
slip-through amount Y, the PM generation amount X is multiplied by
the PM trap efficiency .eta.y to calculate the PM slip-through
amount Y (=X.times..eta.y). A database of the PM trap efficiency
.eta.y is created in advance. A relationship between the amount (PM
trap amount) of PMs trapped in the DPF 19b and the ratio (PM trap
efficiency) .eta.y of the PM trap amount Z to the PM generation
amount X is created and used in the form of, for example, a PM trap
efficiency map as shown in FIG. 9. Also for the PM trap efficiency
map, the PM amounts before and after the DPF 19b are measured to
determine the PM trap efficiency .eta.y in a bench test or the
like, and the PM trap efficiency map is created on the basis of the
cumulative PM trap amount .SIGMA.Z in the DPF 19b. In other words,
a correlation map between the cumulative PM trap amount .SIGMA.Z
and the trap efficiency .eta.y is experimentally created in
advance. The PM trap efficiency .eta.y changes depending on the
cumulative PM trap amount .SIGMA.Z.
The PM generation amount reduction control means M35 is means for
performing a control for limiting the PM generation amount X in the
engine 10, when the PM generation amount X exceeds a preset
acceptable PM generation amount Xc, or when the PM slip-through
amount Y exceeds a preset acceptable PM slip-through amount Yc, in
a temporary period until the surface filtration cake layer has
grown. As the PM generation amount reduction control, a control for
limiting the PM generation amount X by decreasing the EGR rate is
employed. By the control for limiting the PM generation amount X by
decreasing the EGR rate, the in-cylinder combustion temperature is
raised for a temporary period until the surface filtration cake
layer is formed again and has grown to a preset extent. Thus, the
PM generation amount X is reduced, and, in turn, the PM
slip-through amount Y, which is the amount of PMs slipping through
the DPF 19b, is reduced. In this manner, the total amount of PMs
emitted to the atmosphere is reduced. Note that the PM generation
amount limiting control by decreasing the EGR rate leads to the
increase in amount of NOx emitted. This increase can be coped with
by performing a control, such as increasing a reducing agent for a
deNOx catalyst (for example, a urea SCR catalyst) during this
period.
The surface filtration cake layer reformation detection means M36
is means for detecting that the surface filtration cake layer is
formed again, and has grown to a preset extent. The surface
filtration cake layer reformation detection means M36 is configured
to detect that the surface filtration cake layer is formed again,
and has grown to a preset extent at a time point where the PM trap
efficiency .eta.y, which is obtained when the PM slip-through
amount Y is calculated by the PM slip-through amount calculation
means M34, exceeds a preset PM trap return efficiency .eta.yc.
The slip-through amount limiting means M30 is configured to cause
the surface filtration cake layer formation enhancement control
means M32 to select one of the retard control means M32a, the EGR
rate increase control means M32b, and the air-fuel ratio richness
control means M32c according to the operation condition of the
engine, especially the magnitude of the engine torque, and perform
the surface filtration cake layer formation enhancement control in
which the PM generation amount X is increased, when the PM
generation amount X calculated by the PM generation amount
calculation means M33 does not exceed the preset acceptable PM
generation amount Xc, and the PM slip-through amount Y calculated
by the PM generation amount reduction control means M35 does not
exceed the acceptable PM slip-through amount Yc, and also
configured to cause the PM generation amount reduction control
means M35 to perform the PM generation amount reduction control
when the PM generation amount X calculated by the PM generation
amount calculation means M33 exceeds the preset acceptable PM
generation amount Xc, or when the PM slip-through amount Y
calculated by the PM slip-through amount calculation means M34
exceeds the acceptable PM slip-through amount Yc.
Next, an exhaust gas purification method in the above-described
exhaust gas purification system 1 is described with reference to
control flows shown in FIGS. 3 and 4. The control flow in FIG. 3
shows a control for preventing deterioration in emission
performance due to the slip-through of PMs immediately after the PM
re-combustion in the DPF 19b. When the engine 10 starts to operate,
and the forced regeneration treatment of the DPF 19b is started
under control of the exhaust gas purification system 1, the control
flow in FIG. 3 is called by a control flow at a higher level and is
started. In parallel with the forced regeneration treatment, which
is the control flow at the higher level, each step in the control
flows in FIGS. 3 and 4 is performed. Then, the process returns to
the control flow at a higher level. When the forced regeneration
treatment on the DPF 19b is started again, these control flows are
performed in parallel with the forced regeneration treatment. These
control flows are called repeatedly every time the forced
regeneration treatment is performed. With the completion of the
operation of the engine 10, the process returns to the control flow
at the higher level, and the control is stopped.
When the control flow in FIG. 3 is called by the control flow at
the higher level and started, the PM re-combustion completion
detection means M31 determines whether the PM re-combustion is
completed in Step S11. In Step S11, it is determined that the PM
re-combustion is completed at a time point where a value .DELTA.P
detected by the differential pressure sensor 24 becomes smaller
than a preset setting value .DELTA.Pc, or it is determined that the
PM re-combustion is completed at a time point where the PM
concentration difference .DELTA.Cpm across the DPF 19b or the PM
trap efficiency .eta.y calculated from the PM concentration
difference .DELTA.Cpm becomes smaller than the corresponding preset
value .DELTA.Cpm1 or .eta.y1.
If it is determined that the PM re-combustion is not completed in
Step S11 (NO), the process returns to Step S11 after a lapse of a
preset first setting time (time having a relationship with the
interval of the determination in Step S11) .DELTA.t1, and waits for
the completion of the PM re-combustion. If it is determined that
the PM re-combustion is completed in Step S11 (YES), the process
goes to the subsequent Step S12. Note that, upon the completion of
the PM re-combustion, the forced regeneration treatment in the DPF
is stopped by the control flow at the higher level.
In the subsequent Step S12, a control start preparation operation
is performed. In this control start preparation operation, an
elapsed time to of the PM slip-through amount limiting control
starts to be counted, and also the cumulative PM trap amount
.SIGMA.Z is reset to zero. Then, the cumulative PM trap amount
.SIGMA.Z, which is a cumulative value of the PM trap amount Z,
starts to be calculated. In other words, the cumulative value of
the PM trap amount starts to be counted immediately after the PM
re-combustion.
In addition, the PM generation amount calculation means M33
calculates the PM generation amount X generated in the engine
operation state, and moreover, the PM slip-through amount
calculation means M34 calculates the PM slip-through amount Y
through the DPF 19b. For the calculation of the PM slip-through
amount Y, the PM trap efficiency .eta.y is found on the basis of
the cumulative PM trap amount .SIGMA.Z with reference to the PM
trap efficiency map data. Then, from the PM trap efficiency .eta.y
and the PM generation amount X, the PM trap amount Z
(=X.times..eta.y) is calculated, and the PM slip-through amount Y
(=X-Z) trough the DPF 19b is calculated. Here, since the PM trap
efficiency .eta.y varies depending on the cumulative PM trap amount
.SIGMA.Z, .SIGMA.Z=0 is used when Step S12 is performed for the
first time since the control flow in FIG. 3 is called. After that,
the cumulative PM trap amount .SIGMA.Z calculated in Step S14
described later is used.
In the subsequent Step S13, it is determined whether the surface
filtration cake layer formation enhancement control is to be
performed. Specifically, it is determined whether the control for
early formation of the surface filtration cake layer is to be
performed. In other words, it is determined whether the PM
generation amount X and the PM slip-through amount Y are within the
acceptable ranges. In this determination, when the PM generation
amount X calculated by the PM generation amount calculation means
M33 does not exceed the preset acceptable PM generation amount Xc
(X.ltoreq.Xc), and the PM slip-through amount Y calculated by the
PM slip-through amount calculation means M34 does not exceed the
acceptable PM slip-through amount Yc (Y.ltoreq.Yc), it is
determined that the surface filtration cake layer formation
enhancement control is to be performed (YES), and the process goes
to the Step S20. In Step S20, the surface filtration cake layer
formation enhancement control means M32 performs the surface
filtration cake layer formation enhancement control for a preset
second setting time (a time having a relationship with the interval
of the determination in Step S13) .DELTA.t2, and the process goes
to Step S14. In other words, the control for the early formation of
the surface filtration cake layer is performed.
In addition, when the PM generation amount X exceeds the preset
acceptable PM generation amount Xc (X>Xc), or when the PM
slip-through amount Y exceeds the acceptable PM slip-through amount
Yc (Y>Yc), it is determined that the surface filtration cake
layer formation enhancement control is not to be performed (NO),
and the process goes to Step S30. In Step S30, the PM generation
amount reduction control means M35 performs the PM generation
amount reduction control for a second setting time .DELTA.t2, and
the process goes to Step S14. In other words, the PM slip-through
amount Y is reduced by temporarily lowering the EGR rate. The range
where the PM generation amount reduction control is performed is,
for example, the hatched portion of the "PM deterioration region"
on the lower left in the PM generation amount map during ordinary
operation shown in FIG. 5.
Note that when one of the surface filtration cake layer formation
enhancement control and the PM generation amount reduction control
is selected, the other is stopped, and these controls are not
performed simultaneously. Accordingly, when a control is selected
for the first time by the determination in Step S13, the control is
started. When the same control as the preceding control is
selected, the control is continued. When a control different from
the preceding control is selected, the control is switched to the
newly selected control.
Then, as shown in FIG. 4, in the surface filtration cake layer
formation enhancement control in Step S20, it is determined whether
the engine torque T of the engine 10 is lower than the preset first
setting value T1 in Step S21. When the engine torque T is lower,
the engine torque T is determined to be in the low-load region, and
the process goes to Step S23. In Step S23, the retard control means
M32a performs the retard control for a preset third setting time (a
time having a relationship with the second setting time and the
intervals of the determinations in Steps S21 and S20) .DELTA.t3.
Then, the process goes to Step S14 in the control flow in FIG. 3.
In other words, while the temperature of the DPF 19b is monitored,
the HC components in the exhaust gas G are increased by temporarily
retarding the injection timing of the in-cylinder fuel injection
after the temperature drops.
In Step S21, when the engine torque T is not lower than the first
setting value T1, the process goes to Step S22, where it is
determined whether the engine torque T is lower than the preset
second setting value T2. When the engine torque T is lower, the
engine torque T is determined to be in the middle-load region, and
the process goes to Step S24. In Step S24, the EGR rate increase
control means M32b performs the EGR rate increase control for a
third setting time .DELTA.t3. Then, the process goes to Step S14 in
the control flow in FIG. 3. In other words, the growth of the
surface filtration cake layer is enhanced by increasing the EGR
rate to slightly deteriorate the smoke.
When the engine torque T is not lower than the second setting value
T2 in Step S22, the engine torque T is determined to be in the
high-load region, and the process goes to Step S25. In Step S25,
the air-fuel ratio richness control means M32c performs the
air-fuel ratio richness control for the third setting time
.DELTA.t3, and the process goes to Step S14 in the control flow in
FIG. 3. In other words, while the temperature of the DPF 19b is
monitored, the HC components in the exhaust gas G are increased by
temporarily making the air-fuel ratio rich by rich-spike after the
temperature drops.
Thus, when the engine torque T of the engine 10 is lower than the
preset first setting value T1, the retard control can be performed;
when the engine torque T is not lower than the first setting value
T1 but lower than the preset second setting value T2, the EGR rate
increase control can be performed; and when the engine torque T is
not lower than the second setting value T2, the air-fuel ratio
richness control can be performed.
Note that also when anyone of these controls is selected, the other
controls are stopped, and these controls are not performed
simultaneously. Accordingly, when a control is selected for the
first time by the determination in Step S21 or S22, the control is
started. When the same control as the preceding control is
selected, the control is continued. When a control different from
the preceding control is selected, the control is switched to the
newly selected control.
In the surface filtration cake layer formation enhancement control,
the growth of the surface filtration cake layer is enhanced by
slightly deteriorating the smoke immediately after the PM
re-combustion. In this case, the temporary deterioration of PMs
also occurs, but the surface filtration cake layer is formed early
on the wall surface of the DPF 19b. Hence, the total amount of the
emission can be reduced. Here, PM generation amount databases as
shown in FIGS. 5 to 8 are created in advance.
Then, in Step S14 in the control flow in FIG. 3, the PM generation
amount calculation means M33 calculates the PM generation amount X
during the implementation of the Step S20 or Step S30. In other
words, the PM generation amount calculation means M33 calculates
the PM generation amount X generated during the surface filtration
cake layer formation enhancement control or the PM generation
amount X generated during the PM generation amount reduction
control. In addition, the PM slip-through amount calculation means
M34 finds the PM trap efficiency .eta.y on the basis of the
cumulative PM trap amount .SIGMA.Z, which is the cumulative value
of the PM trap amount Z from the start of the counting at the
elapsed time ta, with reference to the PM trap efficiency map data,
then calculates the PM trap amount Z (=X.times..eta.y) from the PM
trap efficiency .eta.y and the PM generation amount X, and
calculates the PM slip-through amount Y (=X-Z) through the DPF
19b.
Then, in the subsequent Step S15, it is determined whether the
surface filtration cake layer formation enhancement control is
completed. This determination is performed on the basis of the two
criteria, namely, whether the elapsed time ta exceeds a preset
setting time tc, and whether the surface filtration cake layer is
formed again and has grown to a preset extent.
The setting time tc is a time during which the differential
pressure across the DPF 19b is raised by about a differential
pressure .DELTA..alpha., which is set in advance as a determination
criterion, to limit the period of the surface filtration cake layer
formation enhancement control or the PM generation amount reduction
control for limiting the PM slip-through amount only to a short
period after the PM re-combustion. The setting time tc is set, for
example, in a range from 3 minutes to 7 minutes (preferably about 5
minutes).
In Step S15, when either it is determined that the elapsed time ta
exceeds the preset setting time tc (t.gtoreq.tc), or the surface
filtration cake layer reformation detection means M36 determines
that the surface filtration cake layer is formed again and has
grown to the preset extent, and the PM trap efficiency .eta.y
exceeds the preset PM trap return efficiency .eta.yc, it is
determined that the surface filtration cake layer formation
enhancement control is completed (YES), and the process goes to the
control completion operation in Step S16.
Meanwhile, when the elapsed time ta does not exceed the preset
setting time tc (t<Tc), and the surface filtration cake layer
reformation detection means M36 does not determine that the surface
filtration cake layer has grown to the preset extent, because the
surface filtration cake layer is formed again, but the PM trap
efficiency .eta.y does not exceed the preset PM trap return
efficiency .eta.yc, it is determined that the surface filtration
cake layer formation enhancement control is not completed (NO), and
the process returns to Step S12. Then, Steps S12 to S16 are
repeated.
In the control completion operation in Step S16, the elapsed time
ta is reset, and also the surface filtration cake layer formation
enhancement control or the PM generation amount reduction control
performed prior to Step S16 is stopped, and the control is returned
to the ordinary operation control in which the EGR control or the
timing control of the in-cylinder fuel injection is performed
according to the engine operation conditions (engine rotation speed
and engine torque) under the current situation. After completion of
the control completion process Step S16, the process goes to
Return, and returns to the control flow at the higher level. In
this manner, the process completes the control flows in FIGS. 3 and
4, and waits for the next implementation of the subsequent forced
regeneration treatment on the DPF 19b.
Note that when the engine 10 stops operating during a control, an
interruption occurs. Even during a control, the process goes to
Step S16, where the control completion operation is completed, and
the process returns to the control flow at the higher level. With
the completion of the control flow at the higher level, these
control flows in FIGS. 3 and 4 are also terminated.
The above-described control makes it possible to temporarily
perform the surface filtration cake layer formation enhancement
control or the PM generation amount reduction control immediately
after the PM re-combustion of the forced regeneration treatment on
the DPF 19b in the exhaust gas purification method in which the
exhaust gas G of the engine 10 is purified with the DPF 19b.
Accordingly, to cope with the phenomenon (blow-off) in which the
amount (PM slip-through amount) Y of PMs passing through the DPF
19b temporarily increases, and the amount of PMs emitted to the
atmosphere temporarily increases immediately after the PM
re-combustion by the forced regeneration treatment of PMs in the
DPF 19b, the early formation and growth of the surface filtration
cake layer on the wall surface of the DPF 19b are enhanced
immediately after the PM re-combustion of the forced regeneration
treatment by the surface filtration cake layer formation
enhancement control in which the PM generation amount X is
increased from that in an ordinary operation during the period for
which this phenomenon continues. Thus, the PM slip-through amount Y
can be reduced, and the total amount of PMs emitted to the
atmosphere can be reduced. In addition, the PM generation amount X
from the engine 10 is reduced for a temporary period until the
surface filtration cake layer has grown by the PM generation amount
reduction control in which the PM generation amount X is increased
from that in an ordinary operation. Thus, the amount of PMs flowing
into the DPF 19b is reduced, and the PM slip-through amount Y
through the DPF 19b is reduced, so that the total amount of PMs
emitted to the atmosphere can be reduced.
In addition, in the exhaust gas purification method, any one of the
PM generation amount increase control by increasing the EGR rate,
the retard control in which the fuel injection timing is retarded
in in-cylinder fuel injection, or the air-fuel ratio richness
control in which the air-fuel ratio is made rich in in-cylinder
fuel injection can be performed as the surface filtration cake
layer formation enhancement control.
Accordingly, in the case of the control for increasing the PM
generation amount X by increasing the EGR rate, the in-cylinder
combustion temperature in a cylinder, the exhaust gas temperature,
and the DPF temperature are lowered by increasing the EGR rate, and
the PM generation amount X is increased. Thus, the formation of the
surface filtration cake layer can be enhanced because of the
increase in the PM trap efficiency .eta.y by the DPF 19b.
Meanwhile, in each of the retard control in which the fuel
injection timing is retarded in in-cylinder fuel injection and the
air-fuel ratio richness control (rich-spike control or the like) in
which the air-fuel ratio is made rich in in-cylinder fuel
injection, the HC components (hydrocarbon components) in the
exhaust gas G are increased by the control, and the HCs are
attached to the PMs to increase the particle diameters. This can
facilitate the trapping of the PMs on the wall surface of the DPF
19b. Thus, the formation of the surface filtration cake layer can
be enhanced.
In addition, in the exhaust gas purification method, the PM
generation amount limiting control by decreasing the EGR rate can
be performed as the PM generation amount reduction control.
Accordingly, by the PM generation amount limiting control by
decreasing the EGR rate, the in-cylinder combustion temperature is
raised, and the PM generation amount is reduced, so that the PM
slip-through amount Y through the DPF 19b can be reduced. Thus,
until the surface filtration cake layer is formed to some extent,
the PM slip-through amount Y can be limited.
Moreover, in the surface filtration cake layer formation
enhancement control in the exhaust gas purification method, the
retard control can be performed when the engine torque T of the
engine 10 is lower than the preset first setting value T1; the EGR
rate increase control can be performed when the engine torque T is
not lower than the first setting value T1 but lower than the preset
second setting value T2; and the air-fuel ratio richness control
can be performed when the engine torque T is not lower than the
second setting value T2.
Accordingly, an optimum surface filtration cake layer formation
enhancement control can be selected according to the engine torque
(engine output) T of the engine 10. Hence, while adverse influences
on the engine torque T and the emission performance are reduced,
the formation of the surface filtration cake layer can be enhanced
efficiently, and the total amount of PMs emitted to the atmosphere
can be reduced.
In addition, in the exhaust gas purification method, the PM
generation amount reduction control can be performed when the PM
generation amount X, which is the amount of PMs generated in the
engine 10 immediately after the PM re-combustion of the forced
regeneration treatment on the DPF 19b exceeds the preset acceptable
PM generation amount Xc, or when the PM slip-through amount Y,
which is the amount of PMs passing through the DPF 19b, exceeds the
preset acceptable PM slip-through amount Yc. Accordingly, the PM
generation amount reduction control is performed on the basis of
the PM generation amount X or the PM slip-through amount Y, and
hence the total amount of PMs emitted to the atmosphere can be
reduced reliably.
Next, effects of the present invention are described by using FIG.
10. FIG. 10 shows an example of a time series of the PM
slip-through amount Y in each of an Example of the present
invention and a Conventional Example of a conventional technology.
A comparison between the DPF outlet soot concentration (PM
slip-through amount) in the "Example" in which the cake layer
formation enhancement was performed immediately after the forced
regeneration treatment on the DPF 19b (with the test time on the
horizontal axis being about 420 seconds to 800 seconds) and the DPF
outlet soot concentration of the conventional technology shows that
the DPF outlet soot concentration was reduced in the Example to
about 1/3 of that in the Conventional Example. It can be understood
that the PM slip-through amount Y was successfully reduced
immediately after the forced regeneration treatment on the DPF 19b,
and the total amount of PMs emitted to the outside air can be
reduced in Example.
Accordingly, according to the exhaust gas purification system 1 and
the exhaust gas purification method configured as described above,
which are directed to the PM slip-through (blow-off) phenomenon in
which the PM slip-through amount Y temporarily increases
immediately after the PM re-combustion of the forced regeneration
treatment on the DPF 19b in the exhaust gas purification system 1
including the DPF 19b disposed in the exhaust passage 13 of the
engine 10, the early reformation and growth of the surface
filtration cake layer on the wall surface of the DPF 19b are
temporarily enhanced by the surface filtration cake layer formation
enhancement control in which the PM generation amount X is
increased, or the PM generation amount X in the engine 10 is
reduced, and the amount of PMs flowing into the DPF 19b is reduced
by the PM generation amount reduction control in which the PM
generation amount X is reduced for a temporary period until the
surface filtration cake layer is formed again and has grown. Thus,
the total amount of PMs emitted to the atmosphere can be reduced
immediately after the PM re-combustion of the forced regeneration
treatment on the DPF 19b, and the total amount of PMs emitted to
the atmosphere can be reduced.
According to the exhaust gas purification system and the exhaust
gas purification method of the present invention, which are
directed to the PM slip-through (blow-off) phenomenon in which the
PM slip-through amount temporarily increases immediately after the
PM re-combustion of the forced regeneration treatment on a DPF in
an exhaust gas purification system including the DPF disposed in an
exhaust passage of an internal combustion engine, the total amount
of PMs emitted to the atmosphere can be reduced immediately after
the PM re-combustion of the forced regeneration treatment of the
DPF, and the total amount of PMs emitted to the atmosphere can be
reduced. Hence, the exhaust gas purification system and the exhaust
gas purification method of the present invention can be used for
internal combustion engines mounted on automobiles, and the
like.
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